Scientific developments during the last decades have created unparalleled opportunities to unravel disease mechanisms and to discover drugs. Unfortunately, many novel targets have binding sites that cannot be modulated with small, drug-like molecules. Instead, compounds with different chemical properties are required, but they must still combine potency and selectivity with cellular permeability that allow them to reach their targets. Our research concerns discovery of such novel, but challenging chemical probes that have potential for development into drugs and is performed at the interface between chemical biology and biomedicine. Our projects focus on how chemical probes for difficult targets should be designed and this insight is then applied to the discovery of probes that are used to elucidate molecular signaling in cancer, chronic kidney disease and rheumatoid arthritis.